On-board measurement of emissions from freight trucks in urban arterials: Effect of operating conditions, emission standards, and truck size

Abstract

Diesel trucks contribute significantly to emissions leading to deterioration in urban air quality. Many recent studies have attempted to quantify real-world emissions from trucks in cities. However, studies on real-world emission from trucks in India are scarce. In this study, we measured real-world emissions of gaseous pollutants (CO, HC, and NO) from twenty trucks of different sizes and emission standards. The trucks were classified into three categories (light-duty diesel trucks (LDDTs), medium-duty diesel trucks (MDDTs), and heavy-duty diesel trucks (HDDTs)) based on their gross vehicle weight (GVW). The tested trucks conformed to Bharat Stage (BS) II, BS III, and BS IV emission standards. A vehicle specific power (VSP) based approach was adopted to model the relationship between vehicle activity and emissions. In addition, real-world emission factors of CO, HC, and NO for all the truck types were determined and compared based on their emission standard. Considerable reductions in emission factors were observed from lower to higher emission control standards for all the pollutants. The CO, HC and NO emission factors from the BS II standard LDDTs were 8.05 g/km, 0.86 g/km, and 8.04 g/km, respectively. The CO emission factor decreased by 29% and 65% respectively, for LDDTs and MDDTs with improved emission standards. The HC emissions (g/km) reduction from BS II to BS III for LDDTs and HDDTs were 49% and 8%, respectively. In the case of MDDTs, HC emission factor reduced by 16% from BS II to BS IV. On comparing with ARAI emission standards, we found that the emission factors of the trucks with GVW less than 3500 kg were higher for all the pollutants. In the case of trucks with GVW greater than 3500 kg, the CO emission factor for BS II and BS III complying trucks were higher than standard values while HC emission factors were lower than the standard values. Further, the emission factors of CO and NO from BS IV standard trucks were higher than the standard values. Moreover, emission factor values from our study were higher than that reported in the literature. Although India aims to adopt BS VI emission standards by 2020, phasing out older vehicles will be the key to mitigate emissions from diesel vehicles.